The present embodiments relate to slice representation of a volume with the aid of volume data.
Imaging methods use a range of different technologies by way of which information about the makeup of an object can be obtained. For example, methods which use ultrasound, X-ray radiation or spin excitations (nuclear spin tomography) are common.
Modern methods can resolve information in three dimensions and supply volume data, which are provided as gray values existing for points in space. For example, the gray values constitute a measure of the density of the examined object at the corresponding point in space. Voxels are also referred to in conjunction with these gray values given at points in space. The voxels form a three-dimensional array of gray values. Voxels defined in three dimensions are mapped onto pixels defined in the two dimensions of a screen for visualization of the result of an imaging method.
The term “volume rendering” has become common for the mapping of voxels onto pixels for display on a screen. In various medical imaging methods, the voxels or gray values are present in what are known as axial slices or sections. Axial slices may be slices orthogonal to a marked direction, as a rule designated the z axis. In computerized tomography, this z axis usually corresponds to the direction of movement. The resolution is usually higher within the axial slices than in the direction of the z axis.
The simplest type of visualization is the displaying of the individual axial slices on a screen. The individual slices may be displayed one after the other, for example. Displaying two to four slice images side by side on an appropriately large screen or monitor is an adequate procedure.
Multi-planar reformatting or multi-planar reconstruction (MPR) provides an extension of the axial slice-based display. Slice representations with a different orientation are calculated within the context of this method. Representation of the sagittal and coronal slices orthogonal to the axial sections is common in this connection. In principle, an MPR method may be carried out for any desired orientation of slices. The gray values within the slices are then calculated by way of interpolation and displayed in a suitable manner.
Apart from the MPR methods, there are other more modern methods. In ray casting, penetration of the volume is simulated using visual rays. Nevertheless, MPR methods fulfill an important function for the visualization of object properties because their use has advantages in certain situations. A suitably selected section may provide information, which can only be accessed with difficulty by ray casting. Ray casting may mask or occlude parts of the object.